1. Field of the Invention
The present invention relates to improved systems and methods for the abatement of industrial effluent fluids, such as effluent gases produced in semiconductor manufacturing processes, while reducing the deposition of reaction products in the treatment systems.
2. Description of the Related Art
The gaseous effluents from the manufacturing of semiconductor materials, devices, products and memory articles involve a wide variety of chemical compounds used and produced in the process facility. These compounds include inorganic and organic compounds, breakdown products of photo-resist and other reagents, and a wide variety of other gases that must be removed from the waste gas before being vented from the process facility into the atmosphere.
Semiconductor manufacturing processes utilize a variety of chemicals, many of which have extremely low human tolerance levels. Such materials include gaseous hydrides of antimony, arsenic, boron, germanium, nitrogen, phosphorous, silicon, selenium, silane, silane mixtures with phosphine, argon, hydrogen, organosilanes, halosilanes, halogens, organometallics and other organic compounds.
Halogens, e.g., fluorine (F2) and other fluorinated compounds, are particularly problematic among the various components requiring abatement. The electronics industry uses perfluorinated compounds (PFCs) in wafer processing tools to remove residue from deposition steps and to etch thin films. PFCs are recognized to be strong contributors to global warming and the electronics industry is working to reduce the emissions of these gases. The most commonly used PFCs include, but are not limited to, CF4, C2F6, SF6, C3F8, C4H8, C4H8O and NF3. In practice, these PFCs are dissociated in a plasma to generate highly reactive fluoride ions and fluorine radicals, which do the actual cleaning and/or etching. The effluent from these processing operations include mostly fluorine, silicon tetrafluoride (SiF4), hydrogen fluoride (HF), carbonyl fluoride (COF2), CF4 and C2F6.
A significant problem of the semiconductor industry has been the removal of these materials from the effluent gas streams. While virtually all U.S. semiconductor manufacturing facilities utilize scrubbers or similar means for treatment of their effluent gases, the technology employed in these facilities is not capable of removing all toxic or otherwise unacceptable impurities.
One solution to this problem is to incinerate the process gas to oxidize the toxic materials, converting them to less toxic forms. Such systems are almost always over-designed in terms of treatment capacity, and typically do not have the ability to safely deal with a large number of mixed chemistry streams without posing complex reactive chemical risks. Further, conventional incinerators typically achieve less than complete combustion thereby allowing the release of pollutants, such as carbon monoxide (CO) and hydrocarbons (HC), to the atmosphere. Furthermore, one of the problems of great concern in effluent treatment is the formation of acid mist, acid vapors, acid gases and NOx (NO, NO2) prior to discharge. A further limitation of conventional incinerators is their inability to mix sufficient combustible fuel with a nonflammable process stream in order to render the resultant mixture flammable and completely combustible.
Oxygen or oxygen-enriched air may be added directly into the combustion chamber for mixing with the waste gas to increase combustion temperatures, however, oxides, particularly silicon oxides may be formed and these oxides tend to deposit on the walls of the combustion chamber. The mass of silicon oxides formed can be relatively large and the gradual deposition within the combustion chamber can induce poor combustion or cause clogging of the combustion chamber, thereby necessitating increased maintenance of the equipment. Depending on the circumstances, the cleaning operation of the abatement apparatus may need to be performed once or twice a week.
It is well known in the arts that the destruction of a halogen gas requires high temperature conditions. To handle the high temperatures, some prior art combustion chambers have included a circumferentially continuous combustion chamber made of ceramic materials to oxidize the effluent within the chamber (see, e.g., U.S. Pat. No. 6,494,711 in the name of Takemura et al., issued Dec. 17, 2002). However, under the extreme temperatures needed to abate halogen gases, these circumferentially continuous ceramic combustion chambers crack due to thermal shock and thus, the thermal insulating function of the combustion chamber fails. An alternative includes the controlled decomposition/oxidation (CDO) systems of the prior art, wherein the effluent gases undergo combustion in the metal inlet tubes, however, the metal inlet tubes of the CDO's are physically and corrosively compromised at the high temperatures, e.g., ≈1260° C.-1600° C., needed to efficiently decompose halogen compounds such as CF4.
Accordingly, it would be advantageous to provide an improved thermal reactor for the decomposition of highly thermally resistant contaminants in a waste gas that provides high temperatures, through the introduction of highly flammable gases, to ensure substantially complete decomposition of said waste stream while simultaneously reducing deposition of unwanted reaction products within the thermal reaction unit. Further, it would be advantageous to provide an improved thermal reaction chamber that does not succumb to the extreme temperatures and corrosive conditions needed to effectively abate the waste gas.